Filling a Pipet

Second, when filling a pipet or volumetric flask, set the liquid s level exactly at the calibration mark. The liquid s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware s calibration mark (Figure 2.6). The meniscus should be adjusted with the calibration mark at eye level to avoid parallax errors. If your eye level is above the calibration mark the pipet or volumetric flask will be overfilled. The pipet or volumetric flask will be underfilled if your eye level is below the calibration mark. 

The device most commonly used to measure volume in general chemistry is the graduated cylinder. A pipet or buret (Figure 1.8) is used when greater accuracy is required. A pipet is calibrated to deliver a fixed volume of liquid—for example, 25.00 mL—when filled to the mark and allowed to drain. Variable volumes can be delivered accurately by a buret, perhaps to 0.01 mL. 

A specimen of the sample is cooled under specified conditions and, at intervals of34°F (1°C), is drawn into a pipet under a controlled vacuum through a standardized wire mesh filter. The procedure is repeated, as the specimen continues to cool, for each 34°F (1°C) below the first test temperature. Testing is continued until the amount of wax crystals that have separated out of solution is sufficient to stop or slow down the flow so that the time taken to fill the pipet exceeds 60 seconds or the fuel fails to return completely to the test jar before the fuel has cooled by a further 34°F (1°C). The indicated temperature at which the last filtration was commenced is recorded as the CFPP. 

When you fdl a buret with fresh solution, it is a wonderful idea to rinse the buret several times with small portions of the new solution, discarding each wash. It is not necessary to fill the buret with wash solution. Simply tilt the buret to allow all surfaces to contact the wash liquid. This same technique should be used with any vessel (such as a spectrophotometer cuvet or a pipet) that is reused without drying. 

To calibrate a 25-mL transfer pipet, you should first weigh an empty weighing bottle like the one in Figure 2-17. Then fill the pipet to the mark with distilled water, drain it into the weighing bottle, and cap the bottle to prevent evaporation. Weigh the bottle again to find the mass of water delivered from the pipet. Finally, use Equation 2-3 to convert mass into volume. 

Mechanical pipet fillers (sometimes called safety pipet fillers, propipets, or pi-fillers) are more convenient than latex bulbs (Figure 1.4C,D). Equipped with a system of hand-operated valves, these fillers can be used for the complete transfer of a liquid. The use of a safety pipet filler is oudined in Figure 1.5. Never allow any solvent or solution to enter the pipet bulb. To avoid this, two things must be kept in mind (1) always maintain careful control while using valve S to fill the pipet, and (2) never use valve S unless the pipet tip is... 

With your thumb and forefinger, press valve S. Liquid will be drawn up into the pipet. By varying the pressure applied by your fingers, the rise of the liquid into the pipet can be controlled. Allow the liquid to fill the pipet to a level slightly above the etched mark on the stem. Release the valve the liquid should remain in the pipet. 

C. Alginate "Snakes" This makes an excellent demonstration on an overhead projector. Fill a crystallizing dish or beaker to a depth of Vi to 3A inch with 2% Ca(N03)2 solution. Introduce a stream of 2% sodium alginate solution directly into the- Ca2+ solution using a pipet. You should be able to cause the formation of a long strand of gel (a snake ). For the most part, the properties of the strands should be the same as those of the beads that you explored above. To test the physical properties of your snakes, wash them in fresh water and let them dry. As they are drying, periodically test their strength and note their appearance. 

Dilute DNA solution to 1-2 ug/ml. in sterile TE and fill the injection pipet by dipping the end in the diluted DNA solution. Allow capillary action to fill the pipet to several millimeters above the tip. Attach the injection pipet to a second micromanipulator via its instrument tube, and connect the instrument tube to a glass 50-mL syringe filled with air. Insert the injection pipet tip into the injection chamber at a 5-10° angle. Demonstrate that the injector is not clogged by displacing an egg with a stream of DNA solution. 

Use a pipet puller to prepare glass transfer pipets so that they are 2-3 cm long with a 120-180 pm diameter, and flame polish the end. Fill the pipet with a small amount of light paraffin oil, then an air bubble, then M2, followed by another air bubble. Fill the pipet with 5-7 eggs, followed by another air bubble and a small amount of M2. 

Sample Solution Fill a 100-mL porcelain crucible halffull of ashless filter paper pulp. Place 2 g of the finished catalyst, in droplet or flake form and accurately weighed, on top of the paper pulp. Transfer the crucible to a muffle furnace set at room temperature, and slowly raise the temperature to 650° so that the stearine melts into the paper, and the organic mass bums and chars slowly. Continue heating at 650° for 2 h or until the carbon is burned off. Cool, add 20 mL of hydrochloric acid, quantitatively transfer the solution or suspension into a 400-mL beaker, and carefully evaporate to dryness on a steam bath. Cool, add 20 mL of hydrochloric acid, warm to aid dissolution (catalysts containing silica will not dissolve completely), transfer into a 500-mL volumetric flask, dilute to volume with water, and mix. Allow any solids to settle, pipet a clear, 50-mL aliquot into a 400-mL beaker, and dilute to 250 mL with water. (If there is suspended matter in the volumetric flask, filter a portion through a dry, medium-speed filter paper into a dry receiver, and pipet from the receiver.)... 

Fill a reservoir with 2 mL of enzyme working solution. Then, using a 12-channel pipetter, add 10 pL to all wells of a flat-bottomed, 96-well fluorescence plate. Using a 12-channel pipeter, 190 pL of substrate/inhibitor solutions in the polypropylene plate are transferred simultaneously to the corresponding well of the fluorescence plate with enzyme. 

Push a small amount of glass wool into the base of a pasteur pipet and fill the pipet with ddH20. As the ddH20 flows out, pipet in the slurry and allow it to pack evenly, making a 1 x 10 cm column. 

Ostwald-Folin pipettes (Figure 1-1, B) are similar to volumetric pipettes but have their bulb closer to the delivery tip and are used for the accurate measurement of viscous fluids, such as blood or serum. In contrast to a volumetric pipette, an Ostwald-Folin pipette has an etched ring near the mouthpiece, indicating that it is a blow-out pipette. With the use of a pipetting bulb, the liquid is blown out of the pipette only after the blood or serum has drained to the last drop in the delivery tip. When filled with opaque fluids, such as blood, the top of the meniscus must he read. Controlled slow... 

Volumetric flasks (Figure 2-20) are manufactured with capacities ranging from 5 mL to 5 L and are usually calibrated to contain a specified volume when filled to a line etched on the neck. They are used for the preparation of standard solutions and for the dilution of samples to a fixed volume prior to taking aliquots with a pipet. Some are also calibrated on a to-deliver basis these are readily distinguished by two reference lines on the neck. If delivery of the stated volume is desired, the flask is filled to the upper line. 

Use a rubber bulb to draw detergent solution to a level 2 to 3 cm above the calibration mark of the pipet. Drain this solution and then rinse the pipet with several portions of tap water. Inspect for film breaks repeat this portion of the cleaning cycle if necessary. Finally, fill the pipet with distilled water to perhaps one third of its capacity and carefully rotate it so that the entire interior surface is wetted. Repeat this rinsing step at least twice. 

Put a bit more sand on top to keep the adsorbent from flying around. Now slowly add the solvent and let it wet the entire column. Dissolve your sample in a minimiun amount of solvent—the least polar solvent it ll dissolve in—and add this solution, slowly, to the top of the pipet. Don t fill the pipet with liquid drip the solution onto the sand. With the sample all on the column, just below the sand, add a small column of elution solvent. This may or may not be different from the solvent you dissolved your sample in. 

In a typical titration experiment, 25.00 mL of 2.000 M HCl is pipetted into an Erlenmeyer flask. A pipet is a piece of glassware that is calibrated to deliver an exact volume of liquid. A solution of NaOH of unknown concentration is placed in a buret (see Figure 11-1), and some is allowed to drain out of the bottom to ensure that the portion below the stopcock is filled. The buret volume is read before any NaOH is added from it to the HCl (say, 3.30 mL) and again after the NaOH is added (say, 45.32 mL). The volume of added NaOH is merely the difference in readings (45.32 mL - 3.30 mL=42.02 mL). The concentration of NaOH may... 

Fill a microtip pipet with tap water, and count the number of drops you can deposit on the penny before water spills over the edge. Record the number of drops. 

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